Hybrid DC magnetic field circuit breaker topology circuit based on capacitor commutation
By using a hybrid DC magnetic field circuit breaker topology based on capacitor commutation, combined with mechanical auxiliary contacts and semiconductor switches, fast and low-loss DC short-circuit current interruption in the excitation circuit of hydropower units is achieved. This solves the problems of arc extinguishing difficulties and high losses in existing circuit breakers without natural zero crossings, and improves the reliability and adaptability of the equipment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-10
- Publication Date
- 2026-03-31
AI Technical Summary
Existing DC circuit breakers in hydropower unit excitation circuits have problems such as lack of natural zero crossing point leading to difficulty in arc extinguishing, high on-state losses, and significant impact on the power grid. Furthermore, existing hybrid DC circuit breakers cannot simultaneously meet the requirements of fast breaking and low loss, and thus cannot satisfy high reliability requirements.
A hybrid DC magnetic field circuit breaker topology based on capacitor commutation is adopted, including a main current-carrying branch, a freewheeling branch, a transfer branch, and an energy absorption branch. It utilizes mechanical auxiliary contacts, silicon carbide MOSFET devices, and IGBT devices to work together to achieve current zero-crossing control and energy absorption, and combines zinc oxide surge arresters to protect semiconductor switches.
It achieves fast, arc-free interruption of DC short-circuit current, reduces conduction losses, minimizes impact on the power grid, and improves equipment reliability and adaptability. It is suitable for DC excitation circuits with frequent adjustments and DC power grid scenarios with high reliability requirements.
Smart Images
Figure CN121769776A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of DC circuit breaker technology, and in particular to a hybrid DC magnetic field circuit breaker topology based on capacitor commutation. Background Technology
[0002] With a high proportion of renewable energy sources exhibiting significant volatility and randomness in the power system, the task of supporting grid stability will shift to traditional synchronous generators such as hydropower units. The operating conditions of hydropower units will tend to be more frequently adjusted, increasing the safety risks of the excitation circuit. The excitation circuit is the core circuit for the regulation and control of hydropower units, and a typical fault it may experience is a short-circuit fault. The primary task of a reliable excitation protection system is for its circuit breakers to quickly and safely interrupt the short-circuit current under extreme short-circuit fault conditions in the excitation circuit. Therefore, high-performance and highly reliable circuit breaker technology is the foundation and most important safety guarantee for the generator control circuit of hydropower units.
[0003] Because the excitation circuit of a hydroelectric generator is a DC circuit and lacks a natural zero-crossing point, traditional magnetic field circuit breakers for excitation circuits are based on mechanical circuit breakers. While these offer low conduction losses, they suffer from low breaking speed, arc erosion during interruption, and a limited number of interruptions. With the development of power electronics semiconductor technology in recent years, using semiconductor switches for short-circuit current interruption has become a current research hotspot. Technical surveys show that while pure solid-state circuit breakers possess fast breaking capabilities, their large conduction losses and the need to simultaneously meet high voltage and high current withstand requirements result in large size, significant heat generation, and relatively weak reliability. Hybrid DC circuit breakers combine the excellent static characteristics of mechanical circuit breakers with the excellent dynamic characteristics of pure solid-state circuit breakers. After the switch is opened, the low on-resistance of the mechanical auxiliary contacts can significantly reduce equipment losses, while simultaneously leveraging the fast breaking capability of the semiconductor switch. However, existing hybrid DC circuit breakers mostly employ simple series-parallel structures, resulting in low commutation efficiency and difficulty in simultaneously meeting the requirements for fast breaking and low losses, thus failing to fully adapt to the high reliability requirements of scenarios such as hydroelectric generator excitation circuits. Summary of the Invention
[0004] In view of this, this application provides a hybrid DC magnetic field circuit breaker topology based on capacitor commutation to solve the problems of existing DC circuit breakers in scenarios such as the excitation circuit of hydropower units, which have difficulty in arc extinguishing, high conduction losses and large impact on the power grid when interrupting DC short circuit current due to the lack of a natural zero crossing point. At the same time, it improves the reliability and adaptability of the circuit breaker under complex operating conditions.
[0005] This application discloses a hybrid DC magnetic field circuit breaker topology based on capacitor commutation, which includes a power supply valve side output terminal and a load side output terminal; the main current-carrying branch, the freewheeling branch, and the transfer branch are all connected in parallel between the power supply valve side output terminal and the load side output terminal; the energy absorption branch is connected to the transfer branch. The main current-carrying branch is used to carry the current under normal operating conditions; the freewheeling branch is used to provide a freewheeling path for the current and ensure that the current transitions smoothly at a specified stage; the transfer branch is used to inject reverse commutation current when a short-circuit fault occurs in the system, so that the current in the main current-carrying branch crosses zero; the energy absorption branch is used to absorb the energy stored in the power system after the short-circuit fault is cut off, suppress overvoltage, and protect the semiconductor switch.
[0006] Furthermore, the main current-carrying branch consists of a mechanical auxiliary contact and an auxiliary converter switch connected in series; the mechanical auxiliary contact and the auxiliary converter switch are respectively connected to the power supply valve side output terminal and the load side output terminal.
[0007] Furthermore, the mechanical auxiliary contact in the main current-carrying branch has the characteristic of low on-resistance, which is used to reduce the on-state loss under normal operating conditions; the auxiliary commutation switch connected in series with the mechanical auxiliary contact is a silicon carbide MOSFET device, which has bidirectional current flow capability and can adapt to the dynamic change of the current direction in the main current-carrying branch during the commutation process. When the auxiliary converter switch receives the turn-off signal, its integrated body diode will naturally turn on, maintaining the current for a period of time, avoiding voltage spikes caused by sudden current interruption, and providing a buffer for a smooth transition in the converter process.
[0008] Furthermore, the freewheeling branch consists of a resistor and a diode; one end of the resistor is connected to the output terminal on the power supply valve side, and the other end is connected to the cathode of the diode, while the anode of the diode is connected to the output terminal on the load side.
[0009] Furthermore, the resistor is used to limit the peak current of the freewheeling branch, and the diode is used to provide a freewheeling path for the reverse current after the main current branch is opened.
[0010] Furthermore, the transfer branch consists of a pre-charge capacitor, a commutation inductor, and a semiconductor switch; one end of the pre-charge capacitor is connected to the output terminal on the power valve side, and the other end is connected to the drain of the semiconductor switch through the commutation inductor, while the source of the semiconductor switch is connected to the output terminal on the load side; the high-potential end of the pre-charge capacitor is connected to the output terminal on the load side, and the low-potential end is connected to the output terminal on the power valve side.
[0011] Furthermore, the pre-charge capacitor in the transfer branch needs to be pre-charged by a DC power supply to a set voltage that matches the system voltage; the commutation inductor is used to limit the rate of rise of the commutation current, avoid damage to the branch components caused by sudden current changes, and ensure the smoothness of the commutation process. Semiconductor switches that work in conjunction with auxiliary commutation switches to perform commutation tasks are used to conduct in case of a fault to inject reverse commutation current. The semiconductor switches use IGBT devices as the core execution unit to adapt to the high-voltage operating conditions of the transfer branch, meet the commutation current injection requirements, stably carry the energy released by the pre-charge capacitor, and adapt to the power level of the transfer branch.
[0012] Furthermore, the energy absorption branch uses a zinc oxide surge arrester (MOV) connected in parallel across the semiconductor switch of the transfer branch to absorb the energy stored in the system and limit overvoltage after the fault is cut off.
[0013] Furthermore, the zinc oxide surge arrester (MOV) has nonlinear volt-ampere characteristics. Under normal operating voltage, it exhibits a high resistance state with leakage current less than the preset value, thus not consuming system energy. When an overvoltage occurs during the commutation process, its resistance rapidly drops to a low resistance state to discharge the overvoltage energy and limit the branch voltage within the device's safe tolerance range. This protects the semiconductor switches in the transfer branch from overvoltage impacts and extends the equipment's service life.
[0014] Furthermore, when the current in the main current-carrying branch drops to zero, the body diode of the auxiliary converter switch, due to its unidirectional conduction characteristic, blocks the reverse current flow. The energy stored in the pre-charged capacitor of the transfer branch needs to find a discharge path. The diode in the freewheeling branch is triggered to conduct when the current in the main current-carrying branch drops to zero and there is a reverse current trend, so that the current flows through the resistor to form a freewheeling circuit. The resistor consumes the remaining electrical energy of the pre-charged capacitor, accelerates the energy decay of the circuit, avoids secondary voltage fluctuations caused by residual energy in the capacitor, and can effectively suppress current peaks, avoid thermal breakdown of the diode due to excessive current, and prevent electrical stress damage to semiconductor devices caused by high current surges, thus ensuring the safe operation of the branch devices during the freewheeling phase.
[0015] Due to the adoption of the above technical solution, this application has the following advantages: 1. This application relies on the low resistance of the mechanical auxiliary contact and the low on-state loss of the silicon carbide MOSFET to significantly reduce the energy consumption of the equipment, reduce the burden on the heat dissipation system, reduce the size of the equipment and reduce the manufacturing cost.
[0016] 2. This application utilizes the IGBT and pre-charge capacitor in the transfer branch to actively make the current in the main current-carrying branch cross zero. Combined with the fast switching characteristics of the silicon carbide MOSFET in the main current-carrying branch, it achieves arc-free interruption of the mechanical auxiliary contact, which can quickly cut off the DC short-circuit current and effectively reduce the impact of faults on the hydropower unit excitation system and the power grid.
[0017] 3. The transfer branch and the energy absorption branch of this application work together to avoid the burning of mechanical contacts by electric arc, extend the life of mechanical circuit breaker, suppress overvoltage through zinc oxide surge arrester, protect semiconductor switching devices, and improve the long-term operational reliability of the overall equipment. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.
[0019] Figure 1 This is a topology diagram of a hybrid DC magnetic field circuit breaker based on capacitor commutation provided in an embodiment of this application.
[0020] Figure 2 This is a timing diagram of the switching device of a hybrid DC magnetic field circuit breaker based on capacitor commutation provided in an embodiment of this application.
[0021] Figures 3(a) to 3(e) This is a schematic diagram of the structure of the hybrid DC magnetic field circuit breaker based on capacitor commutation in operation according to an embodiment of this application. Detailed Implementation
[0022] The present application will be further described in conjunction with the accompanying drawings and embodiments. The described embodiments are only some, not all, of the embodiments of the present application. All other embodiments obtained by those skilled in the art should fall within the protection scope of the embodiments of the present application.
[0023] See Figure 1 This application provides an embodiment of a hybrid DC magnetic field circuit breaker topology circuit based on capacitor commutation, which includes a power supply valve side output terminal C1 and a load side output terminal C2; the main current-carrying branch, the freewheeling branch and the transfer branch are all connected in parallel between the power supply valve side output terminal C1 and the load side output terminal C2; the energy absorption branch is connected to the transfer branch. The main current-carrying branch is used to carry the current under normal operating conditions; the freewheeling branch is used to provide a freewheeling path for the current and ensure that the current transitions smoothly at a specified stage; the transfer branch is used to inject reverse commutation current when a short-circuit fault occurs in the system, so that the current in the main current-carrying branch crosses zero; the energy absorption branch is used to absorb the energy stored in the power system after the short-circuit fault is cut off, suppress overvoltage, and protect the semiconductor switch.
[0024] Optionally, the main current-carrying branch is composed of a mechanical auxiliary contact S1 and an auxiliary converter switch S2 connected in series; the mechanical auxiliary contact S1 and the auxiliary converter switch S2 are respectively connected to the power valve side output terminal C1 and the load side output terminal C2.
[0025] The coordinated operation of each branch in this embodiment achieves rapid, arc-free interruption of DC short-circuit current by using reverse current injection to make the main current-carrying branch current cross zero through internal commutation under a certain time sequence. It also has the advantages of low on-state loss, high reliability, and wide adaptability. It is suitable for DC excitation circuits that require frequent adjustment and have large inductance energy storage characteristics, as well as other DC grid scenarios with high reliability requirements.
[0026] Optionally, the mechanical auxiliary contact S1 in the main current-carrying branch has the characteristic of low on-resistance, which is used to reduce the on-state loss under normal operating conditions; the auxiliary commutation switch S2 connected in series with the mechanical auxiliary contact S1 is selected from silicon carbide MOSFET devices, which have bidirectional current flow capability and can adapt to the dynamic changes in the current direction of the main current-carrying branch during the commutation process. When the auxiliary converter switch S2 receives the turn-off signal, its integrated body diode will naturally turn on, which can maintain the current for a period of time, avoid voltage spikes caused by sudden current interruption, and provide a buffer for a smooth transition of the converter process.
[0027] Specifically, the mechanical auxiliary contact S1 uses a vacuum interrupter, which has low on-resistance and low operating loss, and can interrupt faults under zero current. The auxiliary commutator switch S2 uses a silicon carbide MOSFET, which has bidirectional current flow capability, nanosecond-level switching speed and low on-resistance. When a short-circuit fault occurs, it is used to quickly turn off and provide the conditions for the mechanical auxiliary contact S1 to turn off at zero current.
[0028] Optionally, the freewheeling branch is composed of a resistor R and a diode D; one end of the resistor R is connected to the power valve side output terminal C1, and the other end is connected to the cathode of the diode D, and the anode of the diode D is connected to the load side output terminal C2.
[0029] Optionally, resistor R is used to limit the peak current of the freewheeling branch, and diode D is used to provide a freewheeling path for reverse current after the main current branch is tripped.
[0030] Optionally, the transfer branch consists of a pre-charge capacitor C, a commutation inductor L, and a semiconductor switch S3; one end of the pre-charge capacitor C is connected to the output terminal C1 on the power valve side, and the other end is connected to the drain of the semiconductor switch S3 through the commutation inductor L; the source of the semiconductor switch S3 is connected to the output terminal C2 on the load side.
[0031] Optionally, the high-potential end of the pre-charge capacitor C is connected to the load-side output terminal C2, and the low-potential end is connected to the power valve-side output terminal C1.
[0032] Optionally, the pre-charge capacitor C in the transfer branch needs to be pre-charged by a DC power supply to a set voltage that matches the system voltage; the commutation inductor L is used to limit the rate of rise of the commutation current, avoid damage to the branch components caused by sudden current changes, and ensure the smoothness of the commutation process. The semiconductor switch S3, which works in conjunction with the auxiliary commutation switch S2 to perform the commutation task, is used to conduct in case of a fault to inject reverse commutation current. The semiconductor switch uses IGBT devices as the core execution unit to adapt to the high voltage conditions of the transfer branch, meet the commutation current injection requirements, stably carry the energy released by the pre-charge capacitor, and adapt to the power level of the transfer branch.
[0033] Optionally, the energy absorption branch uses a zinc oxide surge arrester (MOV) connected in parallel across the semiconductor switch S3 in the transfer branch to absorb the energy stored in the system and limit overvoltage after the fault is cut off.
[0034] Optionally, the zinc oxide surge arrester (MOV) has nonlinear volt-ampere characteristics. Under normal operating voltage, it exhibits a high resistance state with leakage current less than the preset value, thus not consuming system energy. When an overvoltage occurs during the commutation process, its resistance rapidly drops to a low resistance state to discharge the overvoltage energy and limit the branch voltage within the device's safe tolerance range, thereby protecting the semiconductor switch S3 of the transfer branch from overvoltage impact and extending the equipment's service life.
[0035] Optionally, when the current in the main current-carrying branch drops to zero, the body diode of the auxiliary commutation switch S2, due to its unidirectional conduction characteristic, blocks the reverse current flow. The energy stored in the pre-charge capacitor C of the transfer branch needs to find a discharge path. When the current in the main current-carrying branch drops to zero and there is a reverse current trend, the diode D is triggered to conduct, allowing the current to flow through the resistor R to form a freewheeling circuit. The resistor R consumes the remaining electrical energy of the pre-charge capacitor C, accelerates the energy decay of the circuit, avoids secondary voltage fluctuations caused by residual energy in the capacitor, and effectively suppresses current peaks, preventing excessive current from causing thermal breakdown of the diode D. It also prevents electrical stress damage to semiconductor devices caused by high current surges, ensuring the safe operation of the branch devices during the freewheeling phase.
[0036] When the system is operating normally, the mechanical auxiliary contact S1 and auxiliary commutator switch S2 are on, the semiconductor switch S3 is off, the pre-charge capacitor C maintains its pre-charge voltage, no current flows through the resistor R and diode D, and the zinc oxide surge arrester MOV is in a high-resistance state due to normal voltage, resulting in minimal leakage current. When a short-circuit fault occurs in the system, the control unit detects the fault current and triggers the auxiliary commutator switch S2 to turn off and the semiconductor switch S3 to turn on. S3 quickly turns on after receiving the signal, forming a complete circuit in the transfer branch. At this time, the energy stored in the pre-charge capacitor C, after being current-limited by the commutator inductor L, is injected into the main current-carrying branch through S3 with a commutation current opposite to the short-circuit current, officially starting the commutation process. As the commutation current gradually increases, it superimposes with the short-circuit current in the main current-carrying branch, reducing the total current in the main current-carrying branch to zero, creating the crucial condition for arc-free tripping of the mechanical auxiliary contact S1. The switch operating sequence is as follows: Figure 2 As shown, Figure 2The horizontal axis t in the diagram represents time. Subsequently, the transfer branch, along with the freewheeling branch and the energy absorption branch, work together to complete the interruption of the fault current and the absorption of energy.
[0037] The working process of the hybrid DC magnetic field circuit breaker based on capacitor commutation is described in detail below: The fault current interruption of the hybrid DC magnetic field circuit breaker of this application is mainly divided into five stages, namely the pre-fault stage, the pre-commutation stage, the commutation stage, the freewheeling stage, and the energy absorption stage. The operating principle of each stage is described in detail below: As shown in Figure 3(a), the pre-fault stage ( t 0≤ t < t 1) When the system is running normally, the mechanical auxiliary contact S1 and the auxiliary converter switch S2 are in the on state, the semiconductor switch S3 is in the off state, the pre-charge capacitor C maintains the pre-charge voltage, the system current flows out through the power valve side outlet C1, flows through the mechanical auxiliary contact S1 and the auxiliary converter switch S2, and flows out through the load side outlet C2, resulting in low operating losses.
[0038] As shown in Figure 3(b), the pre-commutation stage ( t 1≤ t < t 2): t At moment 1, a short-circuit fault occurs in the system, and the fault current rises rapidly. The control unit detects the short-circuit fault and immediately sends a shutdown signal to the auxiliary converter switch S2. The auxiliary converter switch S2 quickly turns off, and its built-in body diode naturally conducts to maintain continuous current and avoid voltage spikes caused by sudden current interruption. At the same time, the control unit sends a conduction trigger signal to the semiconductor switch S3 (IGBT).
[0039] As shown in Figure 3(c), the commutation stage ( t 2≤ t < t 3): t At time 2, semiconductor switch S3 is turned on, forming a circuit in the transfer branch. The pre-charge capacitor C injects a commutation current, opposite in direction to the short-circuit current, into the main current-carrying branch through the commutation inductor L and semiconductor switch S3. After the commutation current and the short-circuit current of the main current-carrying branch are superimposed, the current in the main current-carrying branch begins to decrease rapidly, creating conditions for the arc-free tripping of the mechanical auxiliary contact S1.
[0040] As shown in Figure 3(d), the follow current stage ( t 3≤ t < t 4): tAt time 3, as the commutation current continues to be injected, the current in the main current-carrying branch drops to zero. At this point, the control unit controls the mechanical auxiliary contact S1 to open. Because the current is zero, arc-free opening is achieved, avoiding arc erosion. Due to the body diode characteristics of the auxiliary commutation switch S2, the current will not flow in reverse. The fast recovery diode D in the freewheeling branch conducts, and the reverse current flows through the current-limiting resistor R and the fast recovery diode D in the freewheeling branch, forming an RLC series circuit. The current-limiting resistor R consumes the remaining energy of the pre-charge capacitor C on the one hand, and limits the peak current during the freewheeling process on the other.
[0041] As shown in Figure 3(e), the energy absorption stage ( t > t 4): t At time 4, the mechanical auxiliary contact S1 has reached a sufficient safe disconnection distance. The control system issues a command to lock the semiconductor switch S3 in the transfer branch, and the pre-charge capacitor C no longer injects commutation current into the main current-carrying branch. As the freewheeling process continues, the energy of the pre-charge capacitor C and the inductive components of the system is gradually released, and the voltage across the zinc oxide arrester (MOV) in the energy absorption branch gradually increases. When the voltage across the MOV rises above its operating voltage threshold, the MOV quickly changes from a high-resistance state to a low-resistance state and conducts, and the fault current begins to transfer from the freewheeling branch to the energy absorption branch. Under the nonlinear volt-ampere characteristic of the MOV, the residual current in the line continues to flow through the MOV and gradually decays to zero. The voltage across the MOV drops below the operating voltage, returning to a high-resistance state, and the entire fault clearing process is completed.
[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of the claims of this application.
Claims
1. A hybrid DC magnetic field circuit breaker topology circuit based on capacitive commutation, characterized by, The power supply valve side outlet terminal and the load side outlet terminal are connected by a main current passing branch, a freewheeling branch and a transfer branch in parallel; and an energy absorbing branch is connected with the transfer branch. The main current passing branch is used for bearing the current conduction task under normal conditions; the freewheeling branch is used for providing a freewheeling path for the current and ensuring smooth transition of the current in a specified stage; and the transfer branch is used for injecting a reverse commutation current when a short-circuit fault occurs in the system, so that the current of the main current passing branch passes zero point. The energy absorbing branch is used for absorbing the energy stored in the power system after the short-circuit fault is cut off, suppressing overvoltage and protecting the semiconductor switch.
2. The hybrid DC magnetic field circuit breaker topology circuit based on capacitive commutation of claim 1, wherein, The main current passing branch is composed of a mechanical auxiliary contact and an auxiliary commutation switch in series; and the mechanical auxiliary contact and the auxiliary commutation switch are connected with the power supply valve side outlet terminal and the load side outlet terminal respectively.
3. The hybrid DC magnetic field circuit breaker topology circuit based on capacitive commutation of claim 2, wherein, The mechanical auxiliary contact in the main current passing branch has the characteristics of low conduction resistance and is used for reducing the on-state loss under normal conditions; and the auxiliary commutation switch in series with the mechanical auxiliary contact is selected from silicon carbide MOSFET devices and has the ability of bidirectional current flow, which can adapt to the dynamic change of the current direction of the main current passing branch in the commutation process. When the auxiliary commutation switch receives a turn-off signal, the body diode integrated in the auxiliary commutation switch will be naturally turned on, which can maintain the current for a period of time, avoid the voltage spike caused by the sudden interruption of the current and provide a buffer for the smooth transition of the commutation process.
4. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 1, wherein, The freewheeling branch is composed of a resistor and a diode; one end of the resistor is connected with the power supply valve side outlet terminal, the other end is connected with the cathode of the diode, and the anode of the diode is connected with the load side outlet terminal.
5. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 4, wherein, The resistor is used for limiting the current peak value of the freewheeling branch, and the diode is used for providing a freewheeling path for the reverse current after the main current passing branch is tripped.
6. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 1, wherein, The transfer branch is composed of a pre-charging capacitor, a commutation inductor and a semiconductor switch; one end of the pre-charging capacitor is connected with the power supply valve side outlet terminal, the other end is connected with the drain of the semiconductor switch through the commutation inductor, the source of the semiconductor switch is connected with the load side outlet terminal; the high potential end of the pre-charging capacitor is connected with the load side outlet terminal, and the low potential end is connected with the power supply valve side outlet terminal.
7. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation according to claim 6, characterized in that, The pre-charging capacitor in the transfer branch needs to be pre-charged to a set voltage matched with the system voltage by a direct current power supply; the commutation inductor is used for limiting the rising rate of the commutation current, avoiding damage to the branch devices caused by sudden change of the current and ensuring the stability of the commutation process; The semiconductor switch cooperating with the auxiliary commutation switch to perform the commutation task is used for conducting to inject a reverse commutation current when a fault occurs. The semiconductor switch selects IGBT devices as the core execution unit to adapt to the high voltage working condition of the transfer branch, meet the demand of injecting the commutation current, stably bear the energy released by the pre-charging capacitor and adapt to the power level of the transfer branch.
8. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 1, wherein, The energy absorbing branch adopts a zinc oxide arrester MOV connected in parallel across the semiconductor switch of the transfer branch, which is used for absorbing the energy stored in the system after the fault is cut off and limiting the overvoltage.
9. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 8, wherein, The zinc oxide lightning arrester MOV has a non-linear volt-ampere characteristic, presents a high resistance state at normal operating voltage, and has a leakage current less than a preset value, without consuming system energy; when overvoltage occurs during commutation, the resistance value of the MOV rapidly decreases to a low resistance state, to discharge the overvoltage energy, limit the branch voltage within the safe tolerance range of the device, thereby protecting the semiconductor switch of the transfer branch from overvoltage impact, and prolonging the service life of the equipment.
10. The hybrid DC magnetic field circuit breaker topology based on capacitive commutation of claim 1, wherein, When the current of the main current branch decreases to zero, the body diode of the auxiliary commutation switch blocks the reverse current flow due to its own unidirectional conduction characteristic, and the energy stored in the pre-charging capacitor of the transfer branch needs to find a discharge path. The diode in the freewheeling branch is triggered to conduct when the current of the main current branch decreases to zero and there is a reverse current trend, so that the current flows through the resistor to form a freewheeling circuit. The resistor consumes the remaining energy of the pre-charging capacitor, accelerates the decay of the circuit energy, avoids the secondary voltage fluctuation caused by the residual energy of the capacitor, effectively suppresses the current peak value, avoids the thermal breakdown of the diode caused by excessive current, prevents the electrical stress damage of the semiconductor device caused by high current impact, and ensures the safe operation of the branch device in the freewheeling stage.